Alkane Biodegradation

R. A. Kerr Science 329, 734-735 (2010)

Alkanes

• • • • • Saturated hydrocarbons Large fraction of crude oil Solubility decreases with chain length (straight chains) Can also be branched chains or rings Branched chains are more difficult to degrade than straight chains

Alkane Formula

Methane Ethane Propane Butane Hexane Octane Nonane Decane Dodecane Hexadecane Icosane Triacontane CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 6 H 14 C 8 H 18 C 9 H 20 C 10 H 22 C 12 H 26 C 16 H 34 C 20 H 42 C 30 H 62 Tetracontane C 40 H 82 Pentacontane C 50 H 102 Hexacontane C 60 H 122

Boiling point [°C]

-162 -89 -42 0 69 126 151 174 216 287 343 450 525 575 625 -30 -10 19 37 66

Melting point [°C]

-182 -183 -188 -138 -95 -57 -54 82 91 100

Solubility

63.7

12.3

0.05

5.2 x 10 -5 3.1 x 10 -7

at 20 °C

gas gas gas gas liquid liquid liquid liquid liquid liquid solid solid solid solid solid

n-alkane aerobic degradation pathways

Subterminal oxidation Diterminal oxidation Terminal oxidation H O H O H O O  -oxidation O OH O H O OH O OH OH O OH  -oxidation O OH O H OH OH O O O O O OH + H O O Callaghan 2006, Biodegradation 1990 1:79-92

Aerobic degradation

http://2010.igem.org/Image:TUDelft_Alkane_degradation_route.png

• Oxygen-dependent reactions • Formation of fatty acids, followed by β-oxidation • Biosurfactants may be required before degradation can begin

Branched alkanes

• More difficult to degrade than n-alkanes Appl. Environ. Microbiol. 2000;66:4462-4467

Alkane biodegradation-anaerobic

Environ. Microbiol. 2009 11(10):2477-2490

β-oxidation

http://nutrition.jbpub.com/resources/animations.cfm?id=23&debug=0

Bioremediation

http://www.nies.go.jp/kenko/biotech/bioehp/Topics1.html

Bioremediation

– using biological systems to treat contaminated sites

Biodegradation

– biological activity that results in the break down of a specific contaminant

Bioaugmentation

– adding biodegrading organisms to the contaminated site (not genetically manipulated)

Biostimulation

– adding nutrients like nitrogen or phosphorus in order to stimulate microbial activity

Case study: Deepwater Horizon

• • • • Louisiana crude oil Predominantly alkanes, lower concentrations of aromatics Oil in a large plume near the wellhead, 1 km depth Also surface oil, mobilized oil, reaching shoreline/sensitive wetland areas http://en.wikipedia.org/wiki/File:Deepwater_Horizon_offshore_drilling_u nit_on_fire_2010.jpg April 21, 2010 http://1.bp.blogspot.com/_1p20WdeXKKs/TD VPBQ7NuI/AAAAAAAAJao/7a_bs38l5jE/s200/GulfOilSpillCap1.jpg

Deepwater Horizon-physical/chemical remediation

• Burning – not environmentally smart – greenhouse gases, toxic chemicals released into the atmosphere • Physical removal-does not remove all of the oil; there is water recovered as well, would need to be separated from the oil http://advocacy.britannica.com/blog/advocacy/2010/06 /catastrophe-in-the-gulf-2/ • Chemical dispersion http://www.csmonitor.com/USA/2010/0530/BP -oil-spill-top-kill-failure-means-well-may-gush until-August http://beforeitsnews.com/story/99/939 /What_Is_The_Corexit_Dispersant.ht

ml

Adding dispersant to gushing oil Oil washing up in wetland area E. Kintisch Science 329, 735-736 (2010)

Studying the spill Sample collection

http://www.whoi.edu/oceanus/viewSlideshow.do?clid=58913&aid=105249&mainid=159855&p=157273&n=159853 http://www.whoi.edu/dwhresponse/page.do?pid=43715&tid=201&cid=44272&ct=362# http://oceanexplorer.noaa.gov/explorations/03windows/logs/jul24/media/pushcorealvin.html

Biodegradation concerns

• • • • Bioavailability: – Bacteria are located at the oil-water interface, not inside the oil droplets – Smaller droplets (dispersed oil) give more surface area to increase biodegradation. Explosions in bacterial growth would deplete available nutrients and ultimately slow degradation Oxygen consumption – possible dead zones?

Sedimentation – deposition in anaerobic zones in sediment http://www.mpg.de/257961/Oil_degrading_bacteria?print=yes

Oil-degrading microbes

Image from Hoi-Ying Holman group) • • • • • Hazen et al. (2010) found 2-fold higher cell densities within the plume.

Enrichment in plume for Oceanospirillales Some oxygen depletion in the plume, not enough to create anoxic “dead zones” Enough oxygen loss to indicate aerobic activity Increased degradation genes in plume • Valentine et al. (2010) found oxygen depletion in the plume to be driven by ethane and propane metabolism Oil consuming bacteria on oil droplets, 1500x magnification © Johannes Zedelius, MPI Bremen

Results

http://www.msnbc.msn.com/id/21134540/vp/38853793#38853793